1. Technical Field
Various embodiments of the present invention relates to a flash memory apparatuses and related methods. In particular, certain embodiments relate to a flash memory apparatus and a method for generating a read voltage thereof.
2. Related Art
A flash memory apparatus is a type of semiconductor memory apparatus that is electrically programmable and erasable and requires no refresh operation of rewriting data at constant intervals. The term “program” refers to an operation of writing data to a memory cell, and the term “erase” refers to an operation of erasing data written to a memory cell.
In such a flash memory apparatus, when a program voltage is applied to a control gate through a selected word line, Fowler-Nordheim (F-N) tunneling occurs between a semiconductor substrate and a floating gate, and electrons from a semiconductor substrate flow into a floating gate. In this manner, a program operation is performed. The floating gate into which the electrons flow becomes a programmed cell, and a threshold voltage (Vt) thereof becomes higher than that of an erased cell. The erased cell and the programmed cell can be distinguished by reading a difference of a threshold voltage distribution.
In a conventional flash memory apparatus, however, electrons in an oxide film of a memory cell are trapped during a repetitive F-N tunneling for the program and erase operations, leading to a change in a threshold voltage (Vt) of a memory cell.
Consequently, a flash memory apparatus may incorrectly recognize data stored in a memory cell in a data read operation, causing a degradation in the reliability of a memory cell.